1. Field of the Invention
The present invention relates to a control bus system for use in the control of audiovisual (AV) devices.
2. Description of the Prior Art
Information in a home automation system is transmitted through a control bus system. The home automatic system includes a plurality of various terminals connected to the control bus system, which is controlled by a bus controller. The bus controller controls the transmission of information to and from the terminals, and also effects an exchange of information with external information systems such as telephone lines, cable television (CATV), etc.
One recent trend of home automation is the introduction of a home entertainment system composed of various AV devices including a BS tuner, an FM tuner, a VTR, a laser disc (LD) player, a compact disc (CD) player, a digital audio tape (DAT) player, a cable television (CATV) cable terminal, for example. No problem will arise if these various AV devices are purchased under one brand name for being controlled by one bus controller. However, if a home entertainment system is composed of existing electronic devices that have already been purchased and/or electronic devices of different makes, then the system will have various problems. More specifically, these electronic devices are capable of issuing various control commands. When control commands for similar features are sent from electronic devices to one bus system simultaneously or nearly simultaneously, the bus traffic may be disturbed, the response may become slower, and the operation control process may have errors.
FIG. 1 of the accompanying drawings shows a conventional home entertainment system of such various electronic devices. The home entertainment system includes a CD player 2, an AV selector 3, and a tape deck 4 which are connected to a bus 1. The CD player 2 has a controller 2a and a player mechanism 2b, and the AV selector 3 has a controller 3a and a switcher 3b. When a program source played back by the CD player 2 is to be dubbed by the tape deck 4 through the AV selector 3, the bus 1 allows various functions to be performed as follows:
(a) The tape deck 4 can detect a tape end while it is dubbing the program source played back by the CD player 2.
(b) The CD player 2 can interrupt its playback mode (pause).
(c) The tape deck 4 can reverse the direction in which the tape is recorded.
(d) The CD player 2 can return from any position on a track of a music piece being played back to a point where tracks change, and start playing back the CD after elapse of a desired period of time.
It is assumed that the controllers 2a, 3a of the CD player 2 and the AV selector 3 can issue control commands for the features (c) and (d). When these control commands are transmitted from the controllers 2a, 3a to the bus 1, the tape in the tape deck 4 is reversed by the control command from the controller 2a, and then reversed again by the control command from the controller 3a, so that the tape will run in the original direction. Furthermore, the player mechanism 2b of the CD player 2 may possibly return twice to the point where tracks change. As a consequence, the operation control process suffers errors.
The above features (a) through (d) enable the tape deck 4 to dub the reproduced output signal from the CD player 2 without any dubbed music piece being interrupted.
FIG. 2 shows another conventional home entertainment system composed of a CD player 2, an AV selector 3, a first tape deck 4, and a second tape deck 5. The CD player 2 comprises a controller 2a and a player mechanism 2b. The first tape deck 4 comprises a controller 4a and a tape deck mechanism 4b. The second tape deck 5 comprises only a tape deck mechanism.
In the conventional system shown in FIG. 2, when the reproduced output signal from the CD player 2 is to be dubbed by the first and second tape decks 4, 5, the controller 4a of the first tape deck 4 can recognize a dubbing signal from the CD player 2 and enter a standby mode in response to the dubbing signal. The second tape deck 5 does not have any controller, or it is assumed that even if the second tape deck 5 has a controller, the controller is incapable of recognizing such a dubbing signal. Consequently, the second tape deck 5 cannot read the dubbing command, and cannot dub the reproduced output signal from the CD player 2, resulting in an operation error.
Even when the above errors do not occur, since commands for effecting the same feature are sent to the bus 1, the bus traffic in the bus 1 is increased, and a long period of time is required until the feature is performed. Accordingly, the response of the conventional home entertainment system is poor.